(1) The Field of the Invention
This invention relates to processing apparatus and methods. More precisely, this invention relates to rotary processors particularly useful for processing materials containing dispersed volatiles.
(2) Description of the Prior Art
Rotary processors are known to the art. Details relating to such processors are described in U.S. Pat. Nos. 4,142,805; 4,194,841; 4,207,004; 4,213,709; 4,227,816; 4,255,059; 4,289,319; 4,300,842; 4,329,065; 4,389,119; 4,402,616; 4,411,532; 4,413,913 and 4,421,412.
Essential elements of the basic individual processing passage of rotary processors disclosed in the above patents comprise a rotatable element carrying at least one processing channel and a stationary element providing a coaxial closure surface operationally arranged to form with the channel an enclosed processing passage. The stationary element has an inlet for feeding material to the passage and an outlet for discharge of material from the passage. A member providing a material blocking and material collecting end wall surface is also associated with the stationary element and arranged near the outlet. The end wall surface is adapted to block movement of material fed to the passage and to coact with the moving channel walls to establish relative movement between the blocked material and the moving channel walls. This coaction permits material in contact with the moving walls to be dragged forward to the end wall surface for collection and/or controlled processing and/or discharge.
As disclosed in the above patents, the processing passages present a highly versatile processing capability. The passages are adaptable for performing such processing operations as melting, mixing, pressurizing, pumping, devolatilizing and homogenizing, among others, as well as adding ingredients to or withdrawing ingredients from materials processed in the passage.
U.S. Pat. Nos. 4,227,816; 4,213,709; 4,389,119; 4,402,616 and 4,411,532 relate to multi-stage rotary processors which include a plurality of processing stages, each having one or more processing passages. Material transfer passages or grooves are formed in the closure surface of the stationary element and arranged to transfer material from a passage (or passages) of one stage to a passage (or passages) of another stage.
U.S. Pat. Nos. 4,329,065 and 4,413,913 relate to apparatus and method, respectively, for devolatilizing materials. In accordance with the apparatus and method disclosed therein, material is fed to the processing passage and, near the inlet, the material is collected at a spreading element, builds up pressure and is spread as thin films on the sides of the rotating channel walls. A void space is provided downstream of the spreader and a vacuum source is connected to the void space so that volatile materials can be withdrawn from the surfaces of the thin films carried past the void space. The films may be respread on the channel walls at selected positions about the circumference of the passage to provide more than one void space where the renewed surfaces of the respread films can be exposed to vacuum. The thin films are carried forward through the passage toward the material collecting end wall surface where the films are scraped from the walls, collected and pressurized for discharge. Usually the material is discharged to another devolatilizing passage where it is again spread on the walls and exposed to vacuum in the manner described to achieve the desired degree of devolatilization.
Efficient removal of volatiles from materials is achieved by the method and apparatus disclosed in above-referenced U.S. Pat. Nos. 4,329,065 and 4,413,913. The mass transfer mechanism utilized in the patents primarily involves diffusion of volatiles from the film surfaces during exposure to vacuum or to the inert atmosphere in the void space. In turn, the rate of diffusion of volatiles from the film surfaces--or the volatiles mass transfer efficiency--is dependent on and influenced by such factors as the volatile diffusivity, film thickness, and time of exposure. Thin layers of low viscosity liquid materials provide particularly efficient mass transfer of volatiles from the surfaces of the layers.
U.S. Pat. Nos. 4,389,119; 4,402,616; 4,411,532 and 4,421,412 relate at least in part to apparatus and methods for melting particulate materials. U.S. Pat. No. 4,389,119 discloses a melting stage in which the clearance between the closure surface and the rotor surface portions between melting passages is relatively wide, permitting interchange of material between passages of the stage and providing increased surface area at which melting may take place. A collection channel in the rotor surface is provided outboard of at least one end of the melting stage to control leakage of melted material from the stage. In one embodiment of U.S. Pat. Nos. 4,389,119 and in 4,402,616 and 4,411,532, all of the melting passages discharge material into a common transfer groove for transfer to an adjacent stage. U.S. Pat. No. 4,421,412 discloses an arrangement for a melting passage providing a particulate material restraining surface upstream of the end wall surface and providing control of the space available for the melt pool between the restraining surface and the end wall surface.
This invention is directed to novel improved rotary processors and devolatilizing methods for devolatilization of particulate materials, such as suspension polymerized polystyrene, containing substantial amounts of dispersed volatile component, where the boiling point of the volatiles presents significant problems in separation of volatiles from the material. The processors and methods of this invention provide special advantages in terms of increased devolatilizing efficiency, enhanced quality of product and particularly efficient overall processing performance characteristics.